Such cutting tools, generally in the form of end mills and shell mills, are used in metal working applications in the manufacture of dies and molds and other structures having complex geometrical surfaces and extended shoulders. In these applications it is often required to produce internal corners of small radius, sometimes smaller than 0.5 mm. Generally, complex geometrical surfaces are produced in metal workpieces using ball nose end mills, or end mills with round cutting inserts. There are no ball nose end mills having replaceable cutting inserts that can produce internal corners having a radius as small as 0.5 mm. Also, there are no round cutting inserts having radii as small as 0.5 mm.
When working a large surface of a workpiece, the most economical approach is to use cutting tools having large radii cutting inserts in order to produce the main large scale features of the surface and then to use tools having small radius cutting capability for producing small scale features and for reducing the radii of internal corners where needed.
Cutting inserts having small radius cutting capability are usually rhomboidal in shape, having a cutting nose (or corner) with the required small radius. An example of such a cutting insert and associated cutting tool is disclosed in EP 1 157 768 A1. The cutting insert has a positive geometry and therefore only two cutting corners. DE 28 11 086 A1 discloses an indexable cutting insert for rotary milling machines, consisting of a parallelepiped-shaped body with a parallelogram-shaped cross-section with two faces lying opposite each other, with two edge faces lying between said faces and two front faces lying opposite each other, whereby the faces and the front faces intersect each other and form principal cutting edges, wherein the faces (11, 12) and the edge faces intersect at an angle of less than 90° and form edges (17, 18), a part whereof forms an ancillary cutting edge, whereas the remaining part is provided in the form of a recess (21, 22), which is designed to hold a clamping element, whereby each recess is made by means of smooth faces (23, 24), the extension whereof is limited by edges running parallel to the ancillary cutting edge.
It is an object of the present invention to provide a cutting insert having four cutting corners capable of cutting small radii internal corners in a workpiece. It is also an object of the present invention to provide a cutting tool such as an end mill capable of seating such a cutting insert.
It is a further object of the present invention to provide a cutting insert and a cutting tool, of the aforementioned kind, that is also capable of carrying out ramp down cutting operations.